A rolling resistance of a tire is one of important measurement items for measuring characteristics and performances of tires for a truck, an automobile, and the other vehicles. The rolling resistance of the tire is a force acting between the tire and the ground surface in the tangential direction, and is measured as a force Fx (a change in the rolling resistance Fx when a pressing load Fz is changed) acting between a test tire and a simulation road surface of a drum or the like in the tangential direction in a rolling resistance testing machine.
A typical method of measuring the rolling resistance Fx is a method using a drum type rolling resistance testing machine. The drum type rolling resistance testing machine is configured to measure a relation between the pressing load Fz and the rolling resistance Fx by a multi component force detector (load cell) provided in a spindle shaft supporting a tire while the tire is pressed against a simulation road surface formed in the outer periphery of a running drum.
Specifically, in a case where the rolling resistance Fx is measured, the load fx in the rolling resistance direction is measured by the multi-component force detector provided in the spindle shaft, and Fx may be calculated by “Fx=fx(L/Rd)” (a load method). Here, Rd indicates the radius of the running drum, and L indicates the distance between the axes of the running drum and the tire spindle shaft.
Incidentally, in the rolling resistance testing machine, there is a need to calibrate the multi-component force detector when using the testing machine. In addition, when the multi-component force detector is used for a long period of time, a detection value may have an error. Thus, for example, the multi-component force detector needs to be calibrated every predetermined usage period.
Various methods of calibrating the multi component force detector have been developed. However, as illustrated in Patent Document 1, a calibration may be performed after adding a test load in respective directions using a weight of a given mass. Further, as illustrated in Patent Document 2 or Patent Document 3, there is disclosed a method of performing a calibration by applying an external force through a highly precise load detector.